What happens when a peltier fails?

Question

I am trying to determine all possible failure cases for a heating application with a peltier. Most sources I find on the internet are looking at peltiers as a way of cooling CPUs, so I have heard already that of course they act as an insulator when dead, but I am trying to find out more of the worse-case-scenario of heating effects.

It is unclear from my research whether a failed peltier or an improperly managed peltier ends up effectively being a resistive heater, and if so, is it at the wattage level of the original peltier?

I regularly have used peltiers in heating box applications currently and am trying to design a safer heat box, out of concern that a failed 100W peltier would act as a 100W heater which might create an isolated hotspot (say if the fan also failed) capable of igniting something. But my experience has not validated this theory. In my experience a failed peltier generates less/no heat compared to when it was functioning, not more. But perhaps there are multiple types of failure.

So can anyone give me a straight answer on the possible temperature/error states of a peltier? I am guessing it is something like.

1. Working Peltier: maximum surface temperature on hot-side is a fixed differential over the ambient room temperature on the cold side defined by the heat pump capacity and helped along by a small amount of resistance.
2. Shorted Peltier: becomes a typical resistor, at a wattage dependent on where the short occurred inside? Is this common, possible?
3. Broken Connection Peltier: does nothing if the connection is broken somewhere inside.

Answer 1

My proposed answer is as follows, based on this FAQ plus some physical realities.

The Working state is as described above, as is the Broken Connection state, but the Shorted state is not as has been presented on various over-clocking websites in most heating applications.

Firstly, it appears that peltiers often slowly decline according to the referenced article, with increased resistance and decreased heat pump capacity.

Obviously an all-at-once failure and increase of resistance to the maximum capacity of the device can happen, but that does not mean that the heat produced by a failed 100W peltier in a heating application would be the same as if it were replaced by a 100W resistor as typically used:

Since the peltier will be installed as a heatpump, not a heater, and therefore will have a heatsink or some other ability to exchange temperature on both sides, the total heating capacity will be halved, assuming there were no other variables involved and the installation setup was the same on both the cold and hot side (same heat sink, same fan). But, in reality, since the cold-side will represent an already-colder environment and the hot-side will represent an already-hotter environment it will dissipate heat more quickly and more effectively on the cold side, at least until the two sides eventually equalized in temperature (if that ever occurred).

Therefore, my proposition is that in a typical heating application the heat produced by a perfeclty-shorted 100W peltier would be the equivalent of a 50W, poorly back-insulted, resistance element.